Re: [PATCH v1] iommu/s390: Declare s390 iommu reserved regions

From: Robin Murphy
Date: Thu Jan 17 2019 - 08:02:21 EST

On 15/01/2019 17:37, Pierre Morel wrote:
The s390 iommu can only allow DMA transactions between the zPCI device
entries start_dma and end_dma.

Let's declare the regions before start_dma and after end_dma as
reserved regions using the appropriate callback in iommu_ops.

The reserved region may later be retrieved from sysfs or from
the vfio iommu internal interface.

For this particular case, I think the best solution is to give VFIO the ability to directly interrogate the domain geometry (which s390 appears to set correctly already). The idea of reserved regions was really for 'unexpected' holes inside the usable address space - using them to also describe places that are entirely outside that address space rather confuses things IMO.

Furthermore, even if we *did* end up going down the route of actively reserving addresses beyond the usable aperture, it doesn't seem sensible for individual drivers to do it themselves when the core API already describes the relevant information generically.


This seems to me related with the work Shameer has started on
vfio_iommu_type1 so I add Alex and Shameer to the CC list.

Pierre Morel (1):
iommu/s390: Declare s390 iommu reserved regions

drivers/iommu/s390-iommu.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)